Asking for a woman's Facebook account instead of number.

First, someone may not want to give a link to their website which has a lot of their personal information on it, to a guy who could be a stalker or creep.

Second, asking for a Facebook account is more neutral and for a friend maybe rather than someone you potentially want a relationship with. A phone number is more personal and special rather than being on a list of 300 other people that she rarely talks to. That's a direct trip to the friend zone possibly.

Third, a woman will know that some guys ask for the Facebook because they may lack the confidence to ask for her number.

Four, Facebook takes out one important aspect of flirting: voice. And you can always ask for their phone number if the conversation goes well.